Aerosol dispensing containers have found widespread use in the packaging of fluid materials including a variety of both liquid and powdered particulate products. Such containers are provided with a valve-controlled discharge orifice and operate by the action of a volatile propellant which is confined within the container together with the product to be dispensed. Because the propellant has an appreciable vapor pressure at room temperature, the product in the closed container is maintained under super-atmospheric pressure.
A typical aerosol unit comprises a hollow cylindrical container which is tightly closed at one end and is provided with an opening at its opposite end for receiving a dispensing valve assembly. A closure, commonly referred to as a mounting cup, serves as the closure for the container and as a support for the valve assembly. Typically, the mounting cup comprises a panel having an aperture for receiving the valve assembly a skirt depending from the periphery of the panel, and an annular channel extending outwardly from the edge of the skirt. When the mounting cup is placed in sealing position on the container, the channel is positioned over the bead surrounding the container opening and the lower portion of the skirt adjacent to the channel is flared outwardly against the container wall adjacent the bead. To ensure adequate sealing between the closure and the container, the cup is provided with a gasket which may reside in the annular channel or predominantly in the channel of the cup.
Heretofore, mounting cup gasket seals have been formed by disposing a previously cut gasket in the channel. This type of gasket has the disadvantage of not being stationary relative to the mounting cup during propellant filling or other valve unit assembly operations with the undesirable consequence that when the mounting cup and container are clinched to effect the seal, the gasket is often disposed at an angled position, and thus, the clinching operation is less effective.
Another commercial method for forming the gasket onto the mounting cup consists in forming the gaskets in situ from liquid gasket-forming compositions comprising an elastomer dispersed or dissolved in a volatile organic liquid vehicle. In the manufacture of such a gasket, the liquid composition is deposited in the desired configuration in the channel of the cup while the cup is rotated beneath a metering nozzle through which the composition flows. The deposit is then converted into a dry solid sealing mass by expelling the liquid vehicle at elevated termperatures. Though this technique of flowing gaskets into place has received wide commercial acceptance, it suffers from the disadvantages of requiring the elaborate drying operation, wherein the mounting cup must be handled carefully so as to avoid undue upset from the horizontal; costly recovery apparatus for the expelled organic liquid also must be provided. In sum, the flowed gasket is an expensive step in the formation of the mounting cup. See U.S. Pat. No. 3,342,381 as an example of the "flowed" gasket.
Other techniques for disposing a gasket onto the mounting cup are described in U.S. Pat. No. 3,417,177 wherein the gasket seal is made of heat shrinkable material. After placing a band of gasket material on the skirt, the gasket having a greater diameter than the outside diameter of the skirt of the mounting cup, the cup is heated at a termperature and for a time sufficient to shrink the band into tight frictional engagement with the skirt.
Another similar technique is that disclosed in U.S. Pat. No. 3,443,006, wherein a band of gasket material is swelled through the use of a suitable swelling agent so as to increase its diameter to fit over the skirt of the mounting cup. Subsequently, the swelling agent is removed from the gasket material so that the band will come into tight frictional engagement with the skirt.
Both the heat shrink and swelling techniques for applying a gasket material to the mounting cup have the disadvantage of being costly and relatively time consuming procedures. Note in U.S. Pat. No. 3,417,177, Col. 4, lines 27-31 that the positioned bands must be heated to 240.degree. F. for about 2-3 minutes in order to obtain a tight friction fit. In the procedure of 3,443,006, the bands must stand in the swelling liquid for a period of 1/2 to 11/2 minutes according to example 2 of the '006 patent and then allowed to stand for the drying period. Also in any mass production utilizing the '006 system, an organic liquid recovery system must be employed.